Respiratory health and immune support

How elderflower's flavonoids support respiratory illness, reduce fever, and provide anti-inflammatory and antiviral effects.

Elderflower is the spring blossom of the elder tree (Sambucus nigra) — the same plant that produces elderberries in autumn. While elderberry has received most of the modern research spotlight, elderflowers have centuries of use in European traditional medicine as a remedy for colds, fever, sinus congestion, and sore throats. The flowers contain a distinct set of flavonoids (quercetin, rutin, kaempferol) and phenolic acids that give them genuine anti-inflammatory and antiviral properties [1]. As a warm tea, elderflower acts as a gentle diaphoretic — encouraging perspiration to help break a fever — and supports the respiratory tract during upper respiratory infections.

The flavonoids that do the work

Elderflower's active compounds are primarily flavonol glycosides: quercetin-3-O-rutinoside (rutin), kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside, and isoquercitrin. These account for over 90% of the total flavonoid content in elderflower extracts [5]. Alongside these, phenolic acids including chlorogenic acid and caffeic acid contribute additional antioxidant activity.

These flavonoids work through several interconnected pathways. They inhibit proinflammatory cytokines (TNF-alpha, IL-1-alpha, IL-1-beta), reduce NF-κB activation, and display direct antiviral properties by interfering with the ability of respiratory viruses to attach to and enter host cells. The antiviral mechanism is similar to what has been documented for elderberry: the polyphenols appear to physically bind to viral surface proteins, blocking cellular entry [2].

Diaphoretic and fever-reducing effects

Traditional use of elderflower tea for fevers is well grounded in its pharmacology. A diaphoretic herb increases perspiration, which is the body's primary mechanism for dissipating excess heat during a febrile response. The flavonoids in elderflower contribute to this effect through peripheral vasodilation — widening blood vessels near the skin surface to increase heat loss. Elderflower tea has also traditionally been used as a mild diuretic, supporting kidney function and fluid balance during illness [1].

For a classic preparation: steep 1-2 tablespoons of dried elderflowers in 1 cup of hot (not boiling) water for 10-15 minutes, strain, and drink warm. A teaspoon of raw honey adds both palatability and additional antimicrobial properties.

Respiratory and immune support

Both elderflower extracts and elderberry preparations have been evaluated for respiratory illness. A 2019 meta-analysis of randomized controlled trials found that Sambucus nigra supplementation substantially reduced the duration and severity of upper respiratory symptoms — reduced cold duration by approximately two days on average — with a large mean effect size [2]. A 2021 systematic review confirmed that elderberry is a safe option for viral respiratory illness, with no evidence of dangerous immune overstimulation [3].

While most of these trials used elderberry rather than elderflower specifically, the systematic review of the whole plant [1] confirms that the flowers share the core antiviral and anti-inflammatory mechanisms. In vitro, elderflower aqueous extracts also inhibit the proinflammatory activity of pathogenic bacteria in the mouth and throat, suggesting applications for pharyngitis and oral health [4].

Blood sugar and metabolic properties

Elderflower extracts show meaningful alpha-glucosidase inhibitory activity — the same enzyme target as the diabetes drug acarbose [6]. By slowing the digestion of carbohydrates in the small intestine, elderflower flavonoids can reduce the speed of post-meal glucose absorption. This metabolic effect is complementary to the anti-inflammatory activity: chronic low-grade inflammation and blood sugar dysregulation are closely linked, and compounds that address both simultaneously are particularly valuable. This is preliminary evidence, but it adds to the case for elderflower as more than just a respiratory remedy.

Comparison to elderberry

Elderflower and elderberry complement each other. Elderflower is harvested in late spring before the berries form and is typically used as a tea or tincture. Elderberry (the fruit, harvested in autumn) contains high concentrations of anthocyanins — pigments not present in the flowers — that provide its distinctive antioxidant and antiviral profile. Both parts of the plant support the immune system, but through partially different compounds. Elderflower's flavonol glycosides are particularly suited to respiratory symptoms and fever; elderberry's anthocyanins are more studied for directly inhibiting viral replication.

See our Elderberry page for more on the berry's immune-specific research.

A note on safety: raw elderflowers contain small amounts of cyanogenic glycosides (as do raw elderberries), though in much lower concentrations than the bark, leaves, or unripe berries. Dried elderflowers used for tea are generally considered safe; the drying and heating process degrades these compounds. Avoid consuming large quantities of fresh raw flowers. Elderflower products are not recommended during pregnancy without medical supervision.

Evidence Review

Systematic review and pharmacological overview (Ulbricht et al., 2014) [1]: This comprehensive systematic review by the Natural Standard Research Collaboration covers the full evidence base for both elderberry and elderflower. The review identifies anti-inflammatory, antiviral, diaphoretic, antipyretic, and diuretic properties supported by the botanical literature. It documents the primary flavonoids in elderflowers — rutin, quercetin, isoquercitrin, hyperoside, kaempferol derivatives — and outlines the traditional use evidence alongside limited clinical data. The authors conclude that the evidence for short-term use in respiratory illness is promising, while calling for more rigorous human trials specifically using flower extracts rather than berry preparations.

Meta-analysis of upper respiratory symptoms (Hawkins et al., 2019) [2]: This meta-analysis pooled four randomized controlled trials (total n=180) examining Sambucus nigra supplementation for upper respiratory infections. The quantitative synthesis found a large mean effect size (Cohen's d=0.90) for reduction in upper respiratory symptoms. The analysis specifically noted reductions in congestion, fever, sore throat, and overall symptom burden. Duration of illness was shortened by an average of two days. All included studies used standardized elderberry preparations (primarily syrup or extract, not flower-specific), limiting direct extrapolation to elderflower, but the shared active flavonoid chemistry supports the relevance of findings.

Systematic review of viral respiratory illness (Hawkins, 2021) [3]: This review in BMC Complementary Medicine and Therapies examined the full evidence for elderberry in viral respiratory illness prevention and treatment, including during the COVID-19 era. The review addressed the cytokine storm concern directly: no clinical cases of elderberry-triggered immune overactivation were documented, and available evidence does not support the theoretical risk. The review supports short-term elderberry use as safe and potentially effective for viral upper respiratory infections. It also noted that in vitro studies specifically using elderflower extracts demonstrated antiviral cytokine modulation (reduction of TNF-alpha and IL-1 at relevant concentrations), supporting an active role for the flower preparation.

Anti-inflammatory effects on periodontal pathogens (Harokopakis et al., 2006) [4]: This study examined elderflower aqueous extracts against major periodontal and oral pathogens including Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans. Elderflower extracts significantly inhibited the proinflammatory activities of bacterial virulence factors — specifically their ability to stimulate IL-6, IL-8, and prostaglandin E2 production in human monocytes. The study concluded that elderflower extracts could be useful in modulating the inflammatory response to oral infections. This represents a distinct application from elderberry and is specific to the flower's phytochemistry.

Bioactive properties as a functional ingredient (Sidor & Gramza-Michalowska, 2020) [5]: This comprehensive phytochemical review characterizes Sambucus nigra across its plant parts, with dedicated sections on the flower's composition. Elderflower extracts were found to have high total phenolic content (35-85 mg GAE/g dry weight depending on extraction method) and strong radical-scavenging activity. The review catalogues flavonol glycosides (with rutin dominant at 40-60% of total flavonoids), phenolic acids (chlorogenic acid as the primary representative), and essential oil components (including alpha-linolenic acid, cis-vaccenic acid). The authors note that the flowers' anti-inflammatory and antimicrobial properties are comparably documented to the berries in the scientific literature.

Antidiabetic potential of elderflower extracts (Mikulic-Petkovsek et al., 2024) [6]: This study screened extracts from multiple elderberry cultivars' flowers for their ability to inhibit carbohydrate-digesting enzymes. All tested cultivars demonstrated significant alpha-glucosidase inhibition; three cultivars (Black Beauty, Obelisk, Haschberg) also showed meaningful alpha-amylase inhibition. The mechanism is competitive inhibition of the enzyme active site by quercetin glycosides and chlorogenic acid. IC50 values were in the range of 1.2-3.8 mg/mL for alpha-glucosidase inhibition. While these are in vitro results and clinical trials are still lacking, the findings suggest elderflower tea consumed with or after carbohydrate-containing meals could attenuate post-meal glucose spikes. This adds a metabolic angle to an herb traditionally used only for respiratory purposes.

Overall evidence assessment: The evidence for elderflower's anti-inflammatory, antiviral, and diaphoretic properties is moderately strong at the phytochemical and in vitro level, with clinical support largely coming from elder plant research that spans both berries and flowers. Dedicated clinical trials using flower-specific preparations are limited — most RCTs have used berry extracts. This gap means elderflower should be understood as a traditional remedy with a solid mechanistic rationale and plausible efficacy for respiratory illness, but not yet with the same level of human clinical trial evidence as elderberry. For the specific applications of fever support and mild upper respiratory congestion, its traditional use profile is well supported by its known pharmacology.

References

An evidence-based systematic review of elderberry and elderflower (Sambucus nigra) by the Natural Standard Research CollaborationUlbricht C, Basch E, Cheung L, Goldberg H, Hammerness P, Isaac R, Khalsa KP, Romm A, Rychlik I, Varghese M, Weissner W, Windsor RC, Wortley J. Journal of Dietary Supplements, 2014. PubMed 24409980 →
Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trialsHawkins J, Baker C, Cherry L, Dunne E. Complementary Therapies in Medicine, 2019. PubMed 30670267 →
Elderberry for prevention and treatment of viral respiratory illnesses: a systematic reviewHawkins J. BMC Complementary Medicine and Therapies, 2021. PubMed 33827515 →
Inhibition of proinflammatory activities of major periodontal pathogens by aqueous extracts from elder flower (Sambucus nigra)Harokopakis E, Albzreh MH, Haase EM, Scannapieco FA, Hajishengallis G. Journal of Periodontology, 2006. PubMed 16460254 →
Bioactive properties of Sambucus nigra L. as a functional ingredient for food and pharmaceutical industrySidor A, Gramza-Michalowska A. Food Chemistry, 2020. PubMed 32362939 →
Antidiabetic Potential of Black Elderberry Cultivars Flower Extracts: Phytochemical Profile and Enzyme InhibitionMikulic-Petkovsek M, Stampar F, Schmitzer V. Food Chemistry, 2024. PubMed 39683932 →